Developments in information technology and communications, as well as popularization of computers have led to improvements in semiconductor devices. Larger scale integration of semiconductor devices has spurred research into various methods aimed at reducing the feature size of individual devices formed on a substrate while maximizing performance.
CMOS (complementary metal oxide semiconductor) is a technique that allows larger scale integration of field effect transistors (FET). However, the decreasing dimensions of the FET due to ever larger scale integration results in a decrease in performance or reliability of the devices. To ameliorate these problems, a “fin” FET design has been proposed, characterized by a vertical body structure shaped like a fish's dorsal fin.
Three-dimensional fin FETs may have structural variations, for example, DELTA (fully depleted lean-channel transistor) and GAA (gate all around). A DELTA structure has an active fin-shaped region where a channel is to be formed. The active fin-shaped region protrudes vertically and has a predetermined width. A gate electrode surrounds the vertically protruded channel portion. Thus, the height of the protruded portion becomes the width of the channel and the width of the protruded portion becomes the thickness of the channel. Since both sides of the protruded portion function as a channel, the structure may have the effect of doubling the width of the channel. Accordingly, it is possible to prevent the effective channel width from being decreased while still reducing the overall size of the transistor. Further, since the channel depletion layers form on both sides, overlapping each other, channel conductivity may still be increased even when reducing the feature size of the device.
For instance, in a fin FET having a double gate structure, having the gate electrode at the top and bottom or left and right sides of the channel greatly enhances the current control characteristics in the channel. This means the leakage current between the source and drain can greatly be reduced compared with a single gate device, thereby improving DIBL (drain-induced barrier lowering) characteristics. In addition, the threshold voltage of the device may be varied dynamically by having gates at both sides of the channel. Therefore, the on-off characteristics of the channel may be greatly improved as compared to single gate structures, so that the short-channel effect may be suppressed.
However, the methods for fabricating a fin FET are complex and the current carrying performance is compromised due to further miniaturization of semiconductor devices.